An automatic transmission designed to be mounted on a vehicle is configured to selectively engage a plurality of frictional engagement elements depending on a driving state of the vehicle and thereby change a driving force transmission path from an engine to driving wheels to achieve a plurality of speed stages, and provided with an oil pressure control unit for controlling the engagement of the frictional engagement elements, and an electronic control unit for electrically controlling operation of the oil pressure control unit.
The oil pressure control unit is constructed by attaching a plurality of solenoid valves to a valve body having a control valve mechanism installed therein. In some cases, the electronic control unit is attached to the oil pressure control unit, and they are integrally installed in a casing of an automatic transmission, as disclosed in the following Patent Document 1. The electronic control unit is configured to receive signals from various sensors for detecting the driving state and output a control signal to the solenoid valves of the oil pressure control unit, thereby controlling an engaging oil pressure for each of the frictional engagement elements to automatically change between the speed stages depending on the driving state.
In order to adequately perform the above speed change control, even if a plurality of electronic control units are identical in terms of hardware configuration, a program and/or data for speed change control which vary depending on types of engine, tire and other component of a vehicle to be mounted with an automatic transmission having one of the electronic control units installed therein, or a grade or destination of the vehicle, i.e., depending on an individual specification of the vehicle to be mounted with the automatic transmission, are written to a memory device of each of the electronic control units.    Patent Document 1: JP 2009-85280 A